This invention pertains to the use of N,N-dimethylaminoalkoxypropionitriles as catalysts in the formation of cellular urethane polymers by the reaction of organic polyisocyanates and active hydrogen-containing compounds in the presence of a blowing agent. The invention also relates to particular blended catalysts comprising the said N,N-dimethylaminoalkoxypropionitriles including the use thereof for polyurethane foam formation.
It is well known to the art that cellular urethane polymers are provided by the reaction of organic polyisocyanates and active hydrogen-containing organic compounds such as in particular organic polyols, in the presence of a source of blowing action and one or more activators. It is also known that a number of different chemical reactions occur during polymer formation and expansion. For example, in addition to the chain-extending, urethane-forming reaction between free isocyanate groups and active hydrogen, initially formed urethane linkages bearing secondary hydrogen may also function as a source of active hydrogen and react with additional isocyanate to form cross-links between polymer chains. Further, in systems wherein the blowing agent comprises water such as, for example, flexible, semi-flexible and many rigid foam formulations, isocyanate is also consumed by reaction with water, thereby generating carbon dioxide blowing agent in situ, and introducing further cross-links comprising urea groups. The nature of the cellular structure and the physical and mechanical properties of the foam are influenced by the extent of such reactions, and the relative rates and point in time at which they occur. Although balancing these variables so as to achieve a particular type or grade of foam can be controlled to some extent by the functionality, molecular weight and other structural features of the polyisocyanate and active hydrogen-containing reactants, the catalyst system also plays a significant role in this respect.
Among the types of compounds that have achieved long-standing widespread commercial application as catalysts in polyurethane foam manufacture are: tertiary-amines consisting of carbon, hydrogen and amino nitrogen, as typically illustrated by 1,4-diazabicyclo-[2.2.2]octane ("triethylenediamine"), N,N,N',N'-tetramethyl-1,3-butanediamine and N,N-dimethylcyclohexlamine; tertiary-amines consisting of carbon, hydrogen, amino nitrogen and oxygen wherein oxygen is present as ether oxygen, as typically illustrated by bis[2-(N,N-dimethylamino)ethyl]ether and N-ethylmorpholine; and tertiary-amines consisting of carbon, hydrogen and oxygen wherein oxygen is present as hydroxyl as typically illustrated by N,N-dimethylethanolamine.
More recent advances in cellular urethane manufacture include the utilization of low odor tertiary-amines consisting of carbon, hydrogen, amino nitrogen and oxygen where oxygen is present as carbonyl of either a carboxylate or dimethylamido group, as described and claimed in U.S. Pat. No. 3,821,131, granted June 28, 1974. An especially effective catalyst of this latter type is 3-dimethylamino-N,N-dimethylpropionamide. Another relatively recent advance in the catalysis of cellular urethane manufacture is the use of amine catalyst systems comprising 3-dimethylaminopropionitrile which is also a low odor catalyst. This particular advance is described in U.S. Pat. No. 3,925,268, granted Dec. 9, 1975.
From the standpoint of catalytic activity for the H.sub.2 O/--NCO reaction, the more potent of the aforementioned specific amines are triethylenediamine and bis[2-(N,N-dimethylamino)ethyl]ether. Such catalysts, which are also relatively expensive, are usually supplied and utilized in dilute form as solutions in catalytically inactive diluents such as glycols. Illustrative of such diluents are diethylene glycol and dipropylene glycol.
Of the aforementioned amines, one of the least expensive to manufacture is N,N-dimethylethanolamine ("DMEA") which is readily prepared as the 1:1 molar adduct of dimethylamine and ethylene oxide. Another attractive feature of DMEA is that it is less odorous than many other conventional amines such as N-ethylmorpholine, and those consisting of carbon, hydrogen and amino nitrogen such as, in particular, triethylenediamine and N,N,N',N'-tetramethyl-1,3-butanediamine. Relative to triethylenediamine and bis[2-(N,N-dimethylamino)ethyl]ether, DMEA exhibits moderate activity as a catalyst for water-blown, flexible slabstock. It is often necessary, therefore, in its use in the manufacture of conventional flexible slabstock, to employ DMEA at enhanced concentrations relative to more potent catalysts, in order to meet particular activity and foam property specifications of the foam manufacturer. The use of higher concentrations in turn may enhance any potential deleterious effects of residual amino nitrogen on foam properties. In view of its low cost and low odor, DMEA is typically used in combination with other amines either as a catalytically active diluent for more potent and expensive amines or to "spike" the activity of less potent but more expensive catalysts.
Further in regard to DMEA as well as certain amines of the catalytically potent variety such as triethylenediamine and N,N-dimethylcyclohexylamine, it is found that, whereas they may be suitable for forming conventional flexible and rigid foam, they are unsatisfactory catalysts over a broad range of concentration for the manufacture of void-free, semi-flexible molded foam.
It is also found that certain amines which have widespread application in the manufacture of flexible polyether slabstock such as bis[2-(N,N-dimethylamino)ethyl]ether, have limited application as catalysts in the manufacture of rigid foam blown with fluorocarbon or a combination of fluorocarbon and water.
It is desirable, therefore, and is a primary object of this invention to advance the art of polyurethane foam manufacture by the employment of relatively low cost, low odor N,N-dimethylaminoalkoxypropionitriles which can be used with advantage from the standpoint of: (1) enhanced catalytic activity relative, in particular, to 3-dimethylaminopropionitrile and N,N-dimethylethanolamine; and/or (2) greater versatility in a wide variety of foam formulations including semi-flexible systems, rigid systems blown with fluorocarbon or a combination of fluorocarbon and water, as well as water-blown flexible polyether foam. Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.